I won my second game of the FOTR Constructed League today, and I didn't win any prize at all.
Prizes are awarded (put in your collection) immediately when the match finishes. In addition they are also stored in memory to be shown to you, when you enter some specific places of the website - namely Game Hall and Deck builder. If you did not visit any of these places after you finished your match immediately, and there was a restart of the server (for example today), before you have visited any of those places, you will not see the popup window with the new card/product, however the card/product was added to your collection.
So, what happened here - and I'm guessing - you have won the match, then closed the browser before going to Game Hall, and after some time opened the website again. I have restarted the server in the mean time, so the delivery notification was lost, but the items have been delivered to your collection.